Effect Of Secondary Electron Emission Research Articles

Secondary electron emission in extreme-UV detectors: Application to diamond based devices

A study on the effect of secondary electron emission, which strongly affects the detection of extreme-UV radiation, was performed on diamond detectors. Two different structures were compared: interdigitated contacts and a transverse Schottky diode configuration. Both devices were electrically characterized by I-V measurements and their responsivity was measured in the extreme UV spectral region (20–120 nm) by using He-Ne gas discharge radiation sources and a toroidal grating vacuum monochromator. Through an ad-hoc measurement configuration, the contributions of the internal photocurrent and of the photoemission current have been analyzed and separately evaluated. The results showed that secondary electron emission, which clearly depends on the experimental conditions (e.g., external electric field, pressure, etc.), is one of the most relevant processes affecting the spectral responsivity in the extreme UV band. In particular, for interdigitated devices, extreme care must be taken in order to obtain an absolute value of their responsivity, while detectors in the transverse configuration can be shielded in such a way to avoid secondary electron current contribution and therefore provide a more correct and reliable response.

Hydrogen discharges operating at atmospheric pressure in a semiconductor gas discharge system

Analyses of physical processes which initiate electrical breakdown and spatial stabilization of current and control it with a photosensitive cathode in a semiconductor gas discharge system (SGDS) are carried out in a wide pressure range up to atmospheric pressure p, interelectrode distance d and diameter D of the electrode areas of the semiconductor cathode. The study compares the breakdown and stability curves of the gas discharge in the planar SGDS where the discharge gap is filled with hydrogen and air in two cases. The impact of the ionizing component of the discharge plasma on the control of the stable operation of the planar SGDS is also investigated at atmospheric pressure. The loss of stability is primarily due to modification of the semiconductor-cathode properties on the interaction with low-energy hydrogen ions and the formation of a space charge of positive ions in the discharge gap which changes the discharge from Townsend to glow type. The experimental results show that the discharge current in H2 is more stable than in air. The breakdown voltages are measured for H2 and air with parallel-plane electrodes, for pressures between 28 and 760 Torr. The effective secondary electron emission (SEE) coefficient is then determined from the breakdown voltage results and compared with the experimental results. The influence of the SEE coefficient is stated in terms of the differences between the experimental breakdown law.

Effect of magnetized secondary electron on the characteristics of sheath in Hall thruster

In order to investigate the effects of the inner wall secondary electron emission on the performance of Hall thruster, a hydrodynamic model is used to study the characteristics of plasma sheath considering secondary electron magnetization. The Bohm criterion of the magnetized plasma sheath is obtained. The structures of plasma sheath in Hall thruster with different magnetic field magnitudes and directions, different secondary electron emission coefficients and different plasma species are discussed. Simulation results indicate that both particle density and wall potential increase while the sheath thickness decreases with the augment of secondary electron emission coefficient. The sheath potential and the particle density increase with the magnitude and azimuth angle of magnetic field increasing. Both the sheath thickness and the wall potential are different in different plasma species. These research results provide a theoretical explanation for the magnetism-ampere characteristic of the Hall thruster.

Discharge properties and chemical stability of SrZrO films

Abstract— MgO thin film is currently used as a surface protective layer for dielectric materials because MgO has a high resistance during ion sputtering and exhibits effective secondary electron emission. The secondary‐electron‐emission coefficient γ of MgO is high for Ne ions; however, it is low for Xe ions. The Xe content of the discharge gas of PDPs needs to be raised in order to increase the luminous efficiency. Thus, the development of high‐γ materials replacing MgO is required. The discharge properties and chemical surface stability of SrO containing Zr (SrZrO) as the candidate high‐γ protective layer for noble PDPs have been characterized. SrZrO films have superior chemical stability, especially the resistance to carbonation because of the existence of a few adsorption sites due to their amorphous structure. The firing voltage is 60 V lower than that of MgO films for a discharge gas of Ne/Xe = 85/15 at 60 kPa.

Effects of strong magnetic field on plasma immersion ion implantation of dielectric substrates

In this paper the effects of a strong magnetic field on plasma immersion ion implantation (PHI) of dielectric substrates were investigated. A plasma fluid model and finite difference schemes were used to simulate a one-dimensional system of plasma immersion ion implantation. The effect of secondary electron emission from the electrode on PHI was also taken into consideration. It was found that the magnitude and direction of the magnetic field have slight effects on sheath thickness but have considerable effects on current densities in the y and z directions which are perpendicular to the direction of the electric field (the x direction). The simulations showed that the current densities in the y and z directions increased significantly with increasing magnitude of the magnetic field at a given fixed angle, the reason being attributed to the rotational force exerted on the ions by the magnetic field. With a fixed magnetic field, increasing the angle of the magnetic field, θ, with respect to the electric field produced a continuous increase in current density in the y direction from zero to its maximum at θ = 90° but the current density in the z direction could be described as saddle-shaped being zero at both ends.

Effects of dielectric substrate thickness on plasma immersion ion implantation

A one-dimensional plasma fluid model is developed for investigating the effects of dielectric substrate thickness on plasma immersion ion implantation. By considering the effects of secondary electron emission from the dielectric substrate and using finite difference schemes, evolution of plasma sheath, ion fluence and dielectric surface potential versus time and substrate thickness are evaluated. It was demonstrated that with the increasing dielectric thickness, sheath width and ion fluence over the dielectric surface decrease and surface potential reduces. These effects can be attributed to the accumulation of positive ions and ejection of secondary electrons from the dielectric surface and thereby lessening the strength of the electric field over the dielectric substrate. It is also shown that the secondary electrons have a profound effect on implantation results and must be considered in plasma immersion ion implantation of dielectric materials.

Effect of Secondary Electron Emission on the Sheath in SPT Chamber

A one-dimensional slab model of the plasma sheath in the stationary plasma thruster (SPT) chamber is developed in this study. It is considered that secondary electrons emitted from ceramic walls are partially trapped by the bulk plasma in the SPT chamber; some secondary electrons drift across the sheath where they are generated and the bulk and move towards the opposite sheath. Thus both the secondary electron emission (SEE) from one sheath and the partially trapped secondary electrons from the opposite sheath contribute to this sheath. The results indicate that both the SEE coefficient and trapping coefficient have a significant impact not only on the distributions of both electrons and ions of the SPT sheath but also on the energy flux loss to the SPT wall. When the trapping coefficient increases, the energy flux of electrons deposited to the walls will increase whereas that of ions will decrease. Besides, the critical electron temperature will decrease greatly with the increase of the trapping coefficient.

Jeans instability in the background of secondary electron emission in a complex plasma

In this paper, the effect of secondary electron emission on the Jeans instability in a dusty plasma has been investigated. Owing to secondary electron emission, dust grains may have two stable equilibrium states one of which is negative and the other is positive. In this paper, the case of positive dust grains is reported. Positively charged dust grains attract lighter electrons and repel heavier ions, which resist charge condensation by restricting dust-mass enhancement. As secondary electron emission increases, the dust grains acquire more positive charge and acquire more electrons and repel more heavier ions; this increases the threshold of the Jeans instability. It has been shown that the growth rate of the Jeans instability decreases with increasing secondary electron emission when the equilibrium dust charge is positive.

A PIC-MCC Simulation of the High-Voltage Interruption Ability of a Vacuum Interrupter

In order to examine the ultimate high-voltage interruption ability of a vacuum interrupter, a particle in cell-Monte Carlo collision computer simulation was conducted under the following conditions. Residual charged and neutral particles at current zero were arranged between the electrodes. The particle conditions were obtained from an extrapolated value of experimental data. Secondary electron emission and self-sputtering effects due to ion bombardment were also considered for the simulation. The simulation voltage, which also represents the recovery voltage, was applied between the electrodes. From the results of a simulation on a 168-kV/25-kA 40-mm-diameter one-break interrupter, it was found that the breaking ability is most influenced by the initial neutral particle density. The charged particle density and the secondary electron emission coefficient were found to have a lesser effect on the breaking capability. Consequently, it is estimated that the self-sputtering coefficient from ion bombardment is one of the most important parameters for metal vapor supply after current zero.

Run-to-run variations, asymmetric pulses, and long time-scale transient phenomena in dielectric-barrier atmospheric pressure glow discharges

The dielectric-barrier (DB) discharge is an important approach to generate uniform non-equilibrium atmospheric-pressure glow discharges. We report run-to-run variations, asymmetric pulse formation and long time-scale transient phenomena in these discharges. For similar DB discharge geometric and operating conditions, we observe significant run-to-run variations as manifested in the different voltage–current waveforms at the start of each new run. These run-to-run variations are also accompanied by asymmetric pulses at the start of each run. The variations are observed to drift to a repeatable true steady-state condition on time scales of order tens of minutes to hours. Asymmetric pulse waveforms drift to a symmetric pulse waveform at the true steady state. We explore reasons for these phenomena and rule out thermal drift during a discharge run and gas-phase impurity buildup as potential causes. The most plausible explanation appears to be variations in the surface characteristics of the DBs between two consecutive runs owing to varying inter-run environmental exposure and the conditioning of the dielectric surface during a run owing to plasma–surface interactions. We speculate that the dielectric surface state affects the secondary electron emission coefficient of the surface which in turn is manifested in the discharge properties. A zero-dimensional model of the discharge is used to explore the effect of secondary electron emission.

Kinetic effects in a Hall thruster discharge

Recent analytical studies and particle-in-cell simulations suggested that the electron velocity distribution function in E×B discharge of annular geometry Hall thrusters is non-Maxwellian and anisotropic. The average kinetic energy of electron motion in the direction parallel to the thruster channel walls (across the magnetic field) is several times larger than that in the direction normal to the walls. Electrons are stratified into several groups depending on their origin (e.g., plasma or channel walls) and confinement (e.g., lost on the walls or trapped in the plasma). Practical analytical formulas are derived for the plasma flux to the wall, secondary electron fluxes, plasma potential, and electron cross-field conductivity. Calculations based on these formulas fairly agree with the results of numerical simulations. The self-consistent analysis demonstrates that the elastic electron scattering in collisions with atoms and ions plays a key role in formation of the electron velocity distribution function and the plasma potential with respect to the walls. It is shown that the secondary electron emission from the walls may significantly enhance the electron conductivity across the magnetic field but only weakly affects the insulating properties of the near-wall sheath. Such self-consistent decoupling between the secondary electron emission effects on the electron energy losses and the electron cross-field transport is currently not captured by the existing fluid and hybrid models of Hall thrusters.

Ordered growth of ZnO nanorods for fabrication of a hybrid plasma display panel

Ordered growth of a ZnO nanorod array on a pre-patterned ZnO seed layer was successfullyobtained. This patterned array of ZnO nanorods was introduced to the frontpanel of a plasma display panel (PDP), forming a hybrid PDP. The dischargevoltages of a hybrid panel versus a conventional one were measured, showingsignificantly lower firing and sustaining discharge voltages. The reduction of dischargevoltage was attributed to an enhanced effective secondary electron emission yield(γeff) by the presence ofZnO nanorods. The γeff of a hybrid panel was found to be higher due to the field-assisted electron emissionunder a PDP electrical field. The luminance and luminance efficiency of a hybridPDP were also characterized and compared with those of a conventional panel.

Effect of secondary electron emission on the Jeans instability in a dusty plasma

In this paper the effect of secondary electron emission on Jeans instability in a dusty plasma has been investigated. Due to secondary electron emission, dust grains may have two stable equilibrium states out of which one is negative and the other is positive. Here both cases have been considered separately. It has been shown that secondary electron emission enhances Jeans instability when equilibrium dust charge is negative. It has also been shown that growth rate of Jeans instability reduces with increasing secondary electron emission when equilibrium dust charge is positive.

PIC simulation of N 2 and C 2H 2 plasma behavior around plural objects

The plasma behavior around multiple objects has been simulated for the case of plasma immersion ion implantation (PIII) using the particle-in-cell module of the software “PEGASUS”. Simulations were performed for three types of negative pulse voltage application methods to the objects: (A) a single negative voltage pulse, (B) a negative voltage pulse after a negative voltage pulse, (C) a negative voltage pulse after a positive voltage pulse. The chamber wall was grounded. A cylindrical coordinate system was used. Effects of gas pressure and secondary electron emission by ion impact on the plasma (especially on the density and sheath shape) were studied. The gases were N 2 gas and C 2H 2 gas. The time evolution of the spatial distribution of densities of electrons, N 2 +ions, N 2⁎ radicals, and N atoms in the N 2 plasma, and C 2H 2 +, C 2H 2 2+, C 2H +, CH +, H +, C 2H 2, C 2H, CH 2, CH, H in the C 2H 2 gas plasma, was obtained. The time evolution of flux and energy distribution of electrons and ions at the object surface were also obtained. These results were compared for three types of pulsed voltage application methods, and it was concluded that the C-type was superior for obtaining conformal plasma at the objects.

Effect of secondary electron emission and other sources on the propagation of dust ion acoustic waves in a complex plasma with positively charged dust grains

The effect of secondary electron emission on dust ion acoustic wave (DIA) propagation has been investigated based on orbit motion limited (OML) theory of dust grain charging. The emitted secondaries are assumed to have the same temperature of that of the ambient plasma electrons so that the plasma is effectively composed of three components: The ions, electrons and the varying charged dusts. Together with the effect of secondary electron emission, the effect of ion and electron capture and ionization of neutral atoms and recombination have been included in the ion and electron fluid equations. Small amplitude perturbation is considered about a charge neutral steady state. It is seen that for the positively charged dust grains, waves are purely damped about the equilibrium. The frequency and damping decrement of DIA waves in complex plasmas with positively charged dust grains are determined.

Kinetic simulation of secondary electron emission effects in Hall thrusters

The particle-in-cell code has been developed for kinetic simulations of Hall thrusters with a focus on plasma-wall interaction. It is shown that the effect of secondary electron emission on wall losses is different from predictions of previous fluid and kinetic studies. In simulations, the electron velocity distribution function is strongly anisotropic, depleted at high energy, and nonmonotonic. Secondary electrons form two beams propagating between the walls of a thruster channel in opposite radial directions. The beams produce secondary electron emission themselves depending on their energy at the moment of impact with the wall, which is defined by the electric and magnetic fields in the thruster as well as by the electron transit time between the walls. The condition for the space-charge-limited secondary electron emission depends not only on the energy of bulk plasma electrons but also on the energy of beam electrons. The contribution of the beams to the particles and energy wall losses may be much larger than that of the plasma bulk electrons. Recent experimental studies may indirectly support the results of these simulations, in particular, with respect to the electron temperature saturation and the channel width effect on the thruster discharge.

Measurements of secondary electron emission effects in the Hall thruster discharge

The dependence of the maximum electron temperature on the discharge voltage is studied for two Hall thruster configurations, in which a collisionless plasma is bounded by channel walls made of materials with different secondary electron emission (SEE) properties. The linear growth of the temperature with the discharge voltage, observed in the channel with a low SEE yield, suggests that SEE is responsible for the electron temperature saturation in the thruster configuration with the channel walls having a higher SEE yield. The fact that the values of the electron temperature at saturation are rather high may indirectly support the recently predicted kinetic regime of the space charge saturation of the near-wall sheath in the thruster discharge. A correlation between the effects of the channel wall material on the electron temperature and the electron cross-field current was also observed.

Breakdown Voltage Research of Penning Gas Mixture in Plasma Display Panel

Paschen law and equations, which ignore the influence of the Penning ionization on the electron ionization coefficient (α), are always used as the approximation of the breakdown voltage criterion of the Penning gas mixture in current researches of discharge characteristics of the plasma display panel (PDP). It is doubtful that whether their results match the facts. Based on the Townsend gas self-sustaining discharge condition and the chemical kinetics analysis of the Penning gas mixture discharging in PDP, the empirical equation to describe the breakdown of the Penning gas mixture is given. It is used to calculate the breakdown voltage curves of Ne-Xe/MgO and Ne-Ar/MgO in a testing macroscopic discharge cell of AC-PDP. The effective secondary electron emission coefficients (γeff) of the MgO protective layers are derived by comparing the breakdown voltage curves obtained from the empirical equation with the experimental data of breakdown voltages. In comparison with the results calculated by the Paschen law and the equation which ignore the influence of the Penning ionization on α, the results calculated by the empirical equation have better conformity with experimental data. The empirical equation characterizes the breakdown of the Penning gas mixture in PDP effectively, and gives a convenient way to study its breakdown characteristics and the secondary electron emission behaviors.

Investigation of secondary electron emission effects in plasma immersion ion implantation with dielectric substrates

A one-dimensional fluid sheath model is developed for describing the charging effects with secondary electron emission during plasma immersion ion implantation with dielectric substrates. The temporal evolution of the sheath thickness, surface potential of dielectric substrates and the charge dose accumulated on the surface of dielectric substrates are calculated with the model. The numerical results demonstrate that secondary electron emission effects increase the charging effects greatly, so the sheath thickness becomes thinner and the surface potential of dielectric decreases fast.

The effective secondary electron emission coefficient of MgO protective layer in AC-PDP calculated by fitting breakdown voltage curves

A convenient way is given in this paper to calculate the effective secondary electron emission coefficient ( γ ) of protective layers in AC-PDP by fitting breakdown voltage curves. Based on the analysis of chemical kinetics of gas discharging in Plasma Display Panels, we deduced an empirical equation of self-sustaining discharge condition for Penning gas mixture in terms of Townsend breakdown criteria. It was used to calculate the breakdown voltage curves of Ne-Xe/MgO, Ne-Ar/MgO, Ne/MgO, Ar/MgO and Xe/MgO in a testing macroscopic discharge cell of AC-PDP. The effective secondary electron emission coefficients were derived by comparing the breakdown voltage curves obtained from the empirical equation with the experimental data of breakdown voltages. The γ results showed a good conformity with the secondary electron emission coefficients in literatures. The empirical equation can be used as a convenient approach to research gas discharge characteristics and the effective secondary electron emission behaviors in plasma display panels.